using System;
using System.Data;
using System.Reflection;
using System.Reflection.Emit;

namespace DAL
{
	public class DynamicBuilder<T>
	{
		private static readonly MethodInfo getValueMethod = typeof(IDataRecord).GetMethod("get_Item", new Type[] { typeof(int) });
		private static readonly MethodInfo isDBNullMethod = typeof(IDataRecord).GetMethod("IsDBNull", new Type[] { typeof(int) });
		private delegate T Load(IDataRecord dataRecord);
		private Load handler;

		private DynamicBuilder() { }

		public T Build(IDataRecord dataRecord)
		{
			return handler(dataRecord);
		}

		public static DynamicBuilder<T> CreateBuilder(IDataRecord dataRecord)
		{
			DynamicBuilder<T> dynamicBuilder = new DynamicBuilder<T>();

			DynamicMethod method = new DynamicMethod("DynamicCreate", typeof(T), new Type[] { typeof(IDataRecord) }, typeof(T), true);
			ILGenerator generator = method.GetILGenerator();

			LocalBuilder result = generator.DeclareLocal(typeof(T));
			if (IsSingleType(typeof(T)))
			{
				generator.Emit(OpCodes.Ldarg_0);
				generator.Emit(OpCodes.Ldc_I4, 0);
				generator.Emit(OpCodes.Callvirt, getValueMethod);
				generator.Emit(OpCodes.Unbox_Any, dataRecord.GetFieldType(0));

				generator.Emit(OpCodes.Ret);
			}
			else
			{
				generator.Emit(OpCodes.Newobj, typeof (T).GetConstructor(Type.EmptyTypes));
				generator.Emit(OpCodes.Stloc, result);
				for (int i = 0; i < dataRecord.FieldCount; i++)
				{
					PropertyInfo propertyInfo = typeof (T).GetProperty(dataRecord.GetName(i));
					Label endIfLabel = generator.DefineLabel();

					if (propertyInfo != null && propertyInfo.GetSetMethod() != null)
					{
						generator.Emit(OpCodes.Ldarg_0);
						generator.Emit(OpCodes.Ldc_I4, i);
						generator.Emit(OpCodes.Callvirt, isDBNullMethod);
						generator.Emit(OpCodes.Brtrue, endIfLabel);

						generator.Emit(OpCodes.Ldloc, result);
						generator.Emit(OpCodes.Ldarg_0);
						generator.Emit(OpCodes.Ldc_I4, i);
						generator.Emit(OpCodes.Callvirt, getValueMethod);
						generator.Emit(OpCodes.Unbox_Any, propertyInfo.PropertyType);
						generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod());

						generator.MarkLabel(endIfLabel);
					}
				}

				generator.Emit(OpCodes.Ldloc, result);
				generator.Emit(OpCodes.Ret);
			}

			dynamicBuilder.handler = (Load)method.CreateDelegate(typeof(Load));
			return dynamicBuilder;
		}

		public static bool IsSingleType(Type type)
		{
			return type.IsValueType || type.Name=="String";
		}
	}
}